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Excessive CHT - Help

rvator10

Well Known Member
Patron
Hello and sorry if this topic has already been discussed,
I have a new build -7A with a new Lycoming XIO-360 engine and snorkel inlet.
My first flight (5 minutes) the CHT's hit 550F and I quicky landed.
It was a cool 70F morning and test altitude was 1400-3500 ft.
All the baffling (new)appears perfect with little to no leaking.
I'm just staring my investigation and my first question is (did you install the lower cowling louvers?)
I did not, and that's my starting point for correction.
All suggestions are welcome:confused:
 

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Do you have a larger picture, am I gathering that all of your CHT's went above 500?

I currently have my cowling louvers taped off and honestly I don't know that they really do much for cooling as my temps are still very normal. Hasn't been super hot out yet though.
 
CHT overtemp

The chart you posted is really hard to see the individual data but it does appear to be a very serious CHT overtemp if the sensors are reporting correctly. You might want to give Mike Busch at Savvy Aviation a call for his expert advice. At a minimum would recommend boroscoping all cylinders looking for piston, valve and bore condition. I would drain oil and send it out for analysis and go from there depending on results. You may get away without a complete teardown.
I would not consider even running the engine until you have those tasks done.
There are a number of factors that could cause high CHTs, ignition timing, lean mixture, high power at low airspeed, leaking baffling etc. An RV-7(A) with one occupant light fuel load and a (I)O360 can climb out quite respectably on 24inches of MP and 2400 RPM at 120 knots with a new engine to keep the CHTs below 420 so keeping the speed up and the power down is all goodness with a new engine. The fuel flow should be 16+ gph at full rich under those conditions.
Its good that you have data recorded to aid in the analysis and determination of best course of action going forward.

KT
 
Could you post the raw data in a text file ?

First of all, have you validated the signal levels by placing one of the thermocouples in boiling water and in a glass with ice cubes ? These 2 points should tell you if the system is properly calibrated.

What is the blue signal curve that starts out much lower ?
 
Do Not

Cut your cowl and add louvers ….. removing air isn’t your issue, they really don’t do much in my experience/opinion.

If new engine, has it been broken in using factory protocols?
 
lots of Q&A

I don't suspect instrumentation error, there are 10 thermocouples that read within 5F in a nominal condition, during operation the egt, oat and oil temp all read normal values, but can perform the ice/hot water testing. all other temps seem to be in line, oil 200, egt 1200, oat 70.
the lower line on the chart is % power, see y axis RHS.
the file attach feature looks like it will only handle pictures not Excell files, so help...
the new engine test run log had 1 hr 20 min and at 2700 rpm 425ish CHT.
I haven't verified the timing yet (both are magnetos) and should be 25 BTDC.
thx
 
Getting to 550 that quickly….I have to echo the thoughts to check timing - in all my years of running these engines, that is what seems to quickly create very high temps most quickly. And it is so easy to think you have it right when in fact, it is way off.
 
I agree with Paul that timing is likley the issue. My new IO-360 M1B was shipped with the mag timing 3 to 4 degrees advanced. I would recommend checking mag timing on all new factory engines before first startup.
 
I would be looking at instrumentation anomolies. 550 in a couple minutes is insanely high. I don't see how too much advance could drive temps that high. You can only advance so much and then power and temps fall off. Can't read your chart, so that limits my thoughts. If no instrument errors, next guess would be detonation. That WILL drive up temps very fast. Detonation can occur at full power with too much advance. Detonation causes a VERY rapid rise in CHTs. Again, can't read chart to assess.

You sure you select the correct thermocouple type in the EIS? Some systems, such as G3X, allow both types for CHT and if set wrong, can read in the ballpark at low temps and way off at high temps.

Larry
 
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CHTs

I don't suspect instrumentation error, there are 10 thermocouples that read within 5F in a nominal condition, during operation the egt, oat and oil temp all read normal values, but can perform the ice/hot water testing. all other temps seem to be in line, oil 200, egt 1200, oat 70.
the lower line on the chart is % power, see y axis RHS.
the file attach feature looks like it will only handle pictures not Excell files, so help...
the new engine test run log had 1 hr 20 min and at 2700 rpm 425ish CHT.
I haven't verified the timing yet (both are magnetos) and should be 25 BTDC.
thx

If the blue line is power then looking at the first two spikes - one may be the mag check and the second prop cycling prior to take-off if you have a CS prop. The CHTs are all at about 400 before take- off which would be a good clue to something being badly out of whack. If you are only seeing EGTs in the 1200 range then that would be another pointer to timing or fuel.
KT
 
If type J thermocouples were used for CHT sensors in a system expecting type K you would see an error about that magnitude and sign.
 
Nose Gear Fairings In Place?

Timing and instrumentation are the most likely culprit to the high CHT’s, but be sure the bottom cowl is closed up where the nose gear leg enters. If the nose gear fairings are not in place for your Phase 1 flights, the hole needs to be taped over. Any air coming into the lower cowl area through that opening destroys the proper upper to lower cooling airflow within the cowl. The air inlets behind the prop need to be properly implemented as well. Extraneous air introduced into the lower cowl must be eliminated.
 
ignition timing

people assume that mags are set and timed on a new engine.
They are not, you have to set them.
 
I'd upload the data to Savvy and then share the link - the gurus on VAF will tell you what's wrong in about 2 mins. From what I can see on your graphs, it seems that there is an instrumentation error. I doubt your engine would have survived that long at 550F.
 
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Check the probe configuration

I saw this exact same scenario at Synergy Air in Eugene a few years back with a new RV-14 on the first flight. Turned out to be incorrectly configured thermocouple probes. Hope that is the case here versus an engine teardown.
 
Timing and instrumentation are the most likely culprit to the high CHT’s, but be sure the bottom cowl is closed up where the nose gear leg enters. If the nose gear fairings are not in place for your Phase 1 flights, the hole needs to be taped over. Any air coming into the lower cowl area through that opening destroys the proper upper to lower cooling airflow within the cowl. The air inlets behind the prop need to be properly implemented as well. Extraneous air introduced into the lower cowl must be eliminated.

Sorry, but leaving the intersection fairing off will NOT cause 550* CHTs.

Larry
 
I don't suspect instrumentation error, there are 10 thermocouples that read within 5F in a nominal condition, during operation the egt, oat and oil temp all read normal values, but can perform the ice/hot water testing. all other temps seem to be in line, oil 200, egt 1200, oat 70.
the lower line on the chart is % power, see y axis RHS.
the file attach feature looks like it will only handle pictures not Excell files, so help...
the new engine test run log had 1 hr 20 min and at 2700 rpm 425ish CHT.
I haven't verified the timing yet (both are magnetos) and should be 25 BTDC.
thx

What probe types do you have specified in your EFIS/EIS for CHT - Either Type J or Type K?

Does that match the actual probe? Type K probe will have Yellow & Red wire, Type J will have White & Red wire (some are black & red).

Also, does the lead-in wire from the probe to the EIS connector match (Red/Yellow or White/Yellow) the wire from the probe?
 
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some more checks

the G3X GEA kit uses type K factory probes, I purchased type k wire, same as my last RV with the same G3X configuration, I checked the set up this AM and its correct, set-in type K, not J. I also performed the Ice/boiling water test on one CHT sensor and had 33-35F and 205-210F, so I'm convinced the instrumentation is configured and working correctly.
I reinspected the baffling and I still don't see any issues. my next step is to break out my speed tape and start covering anything I can that will help with baffling to cowl interface. i need to parking lot the airplane for other headwinds so I will be offline for 2-3 wks.
thx for your help
 
the G3X GEA kit uses type K factory probes, I purchased type k wire, same as my last RV with the same G3X configuration, I checked the set up this AM and its correct, set-in type K, not J. I also performed the Ice/boiling water test on one CHT sensor and had 33-35F and 205-210F, so I'm convinced the instrumentation is configured and working correctly.
I reinspected the baffling and I still don't see any issues. my next step is to break out my speed tape and start covering anything I can that will help with baffling to cowl interface. i need to parking lot the airplane for other headwinds so I will be offline for 2-3 wks.
thx for your help

You need someone knowledgable with engines to help you. While baffling quality can move the needle on cooling efficiency, I am convinced that even the worst baffling quality could not produce CHTs of 550, with all else being normal. Birds nest, sure, but not the typical flaws we see. To give you an example, I accidentally left the cowl plugs in for the first time a couple of months ago. That is ZERO cooling flow and the CHTs only got to 425 beyond pattern altitude. I am confident that would have climbed higher had I not noticed and pulled the power back. If I can go a full minute with NO cooling and only get to 425, how is it possible that you got to 550 in 3-4 minutes WITH cooling flow? Something is producing VERY HIGH volumes of heat and you need to find it.

Larry
 
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If the engine truly got to 550 at a minimum it needs a inspection. I would at least contact the builder or lycoming and get their thoughts.
 
the G3X GEA kit uses type K factory probes, I purchased type k wire, same as my last RV with the same G3X configuration, I checked the set up this AM and its correct, set-in type K, not J. I also performed the Ice/boiling water test on one CHT sensor and had 33-35F and 205-210F, so I'm convinced the instrumentation is configured and working correctly.
I reinspected the baffling and I still don't see any issues. my next step is to break out my speed tape and start covering anything I can that will help with baffling to cowl interface. i need to parking lot the airplane for other headwinds so I will be offline for 2-3 wks.
thx for your help

If the instrumentation has been checked and verified, the next step should be to confirm no issue with the engine. Next thing I would check (as already mentioned by many others) is to confirm the ignition timing. Perhaps have someone else check with you.

Poor baffling (unless grossly so) would not be a cause for CHTs going over 500 F in 5 minutes.
 
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